Your question is a bit confusing. I'm not sure if your concern is on signatures or photos in general. That is, putting a photo in your signature is not the same as not having to download images in inbox. Anyhoo, here is some info of possible use:
To put a photo in your signature, just go to Account>Properties>Templates>New Templates. That window has a tool bar and on right side you will see >> and placing mouse over it, the text 'more buttons' appears. (If you don't see the >>, open the window a bit wider.) Click and a drop-down menu appears and one entry is 'Insert image'. Click that and you can then insert photo. Tips:
a. Have cursor positioned in template where you want photo inserted FIRST.
b. Photo needs to be sized prior to doing this so that it fits properly in signature area
c. Photo will only appear in outgoing emails when you write in HTML or HTML/text mode.
I don't know situations where you must download images, so it may help to explain that. With HTML viewer, they're immediately visible. If images are on sender's server, TB! asks that you decide whether to download or not.
I do hope you find this useful. Daniel's response may have been what you sought, but now you at least have info for creating photos in messages and also in your signature. Good luck.